Microelectronic devices such as semiconductor devices are generally fabricated on and/or in substrates or wafers. In a typical fabrication process, one or more layers of metal or other conductive materials are formed on a wafer in an electroplating processor. The processor may have a bath of electrolyte held in vessel or bowl, with one or more anodes in the bowl. The wafer itself may be held in a rotor in a head movable into the bowl for processing and away from the bowl for loading and unloading. A contact ring on the rotor generally has a large number of contact fingers that make electrical contact with the wafer. A membrane may be positioned in the bowl between the anodes and the wafer, as described in U.S. Pat. Nos. 7,585,398 and 7,264,698, incorporated herein by reference. The membrane allows certain ions to pass through, while blocking passage of other molecules, which can provide improved electroplating results and performance.
In many electroplating processors, the membrane is supported on the top and the bottom via mechanical supports as shown for example in FIG. 5 of U.S. Patent Publication No. 2012/0292181. However, certain newer processors are designed to be much shorter, so that the processors may be stacked on two levels of a processing system. The stacked two level processing system may have twice as many processors as a single level processing system, effectively doubling processing capacity in many applications, while requiring little or no additional clean room space. Conventional membrane supports though are not suitable for use in these compact processors because they are too large in the vertical dimension, taking up too much height in the bowl.
Gas bubbles in the electrolyte may tend to nucleate or adhere to the surfaces of conventional membrane supports. Gas bubbles are a leading cause of wafer defects in the electroplating process. In processors having a relatively large vertical space between the membrane supports and the wafer, such as the processor described in U.S. Patent Publication No. 2012/0292181, gas bubbles on the membrane supports are generally not a significant disadvantage because their effects at the wafer are reduced by the relatively large spacing between them.
On the other hand, in current compact processor designs having much more limited vertical dimension, the membrane is necessarily much closer to the wafer. As a result, in these types of processors gas bubbles present a significant engineering challenge.
The membrane material can significantly expand when wetted. It may also stretch when subjected to liquid pressure forces in the bowl, such as pressure differences in the catholyte above and the anolyte below the membrane. The membrane, if not supported, may therefore tend to sag or wrinkle, which contributes to gas bubble trapping and interference with fluid flow within the chamber. Accordingly, improved processors and methods are needed.